Some GMAT Focus questions definitely appear in OG 12
and the GMAT Quant Review guide, but I don't think that there's much overlap between the GMATPrep and GMAT Focus. GMAC claims that the GMAT Focus doesn't overlap OG 13
at all, though. If you've already gone through OG 12
and the Quant Review Guide, you'll probably find that roughly 25% of the GMAT Focus questions are familiar.
The good news is that GMAT Focus includes answer explanations. I think they owe you that, considering the price of GMAT Focus ($29.99 for a 24-question test).
Have fun studying!
Helping students kick the GMAT in the nuts since 2002... www.gmatninja.com.